The present invention relates to an inflator for an inflatable airbag of a vehicle occupant restraint system.
In vehicle occupant restraint systems, an airbag is inflatable by an inflation fluid from an inflation fluid source stored in an airbag inflator upon a collision.
Various types of inflators for vehicle inflatable airbags are well known. Among them, one type of inflators include a housing, a solid gas generant filled in the housing, a heat-producing material enclosed in the gas generant, an ignitor material disposed at one end portion of the housing, and a filter disposed between the housing and the gas generant. A plurality of gas outlet,ports are formed in a circumferential wall of the housing. The solid gas generant is a material thermally decomposable to generate an inflation gas for inflating the airbag. For instance, the solid gas generant is sodium azide thermally decomposable to generate a nitrogen gas as indicated by the following formula: EQU NaN.sub.3 .fwdarw.Na+3/2.multidot.N.sub.2
The ignitor material is a pyrotechnic, for example, a powdery mixture of zinc perchlorate and potassium perchlorate, which is adapted to ignite in response to an electrical signal generated upon a vehicle collision. The heat-producing material is, for example, a pyrotechnic including boron potassium nitrate powder. The heat-producing material increases heat generated by the ignition of the ignitor material to thermally decompose the solid gas generant. The filter is provided for cooling the inflation gas resulting from the thermal decomposition of the solid gas generant and for trapping solid products which are generated by the thermal decomposition together with the inflation gas, to prevent the by-products from entering the airbag and a vehicle occupant compartment.
In this type of the inflator, it takes a relatively long period of time from ignition of the ignitor material in response to the electrical signal to generation of the inflation gas from the gas generant. The inflator of such type is required to use a sensor for reducing the relatively long period of time, which influences other components of the inflator. In addition, by the reason of using the ignitor material to cause the thermal decomposition of the gas generant, the conventional type of the inflator has a substantial limitation with respect to the arrangement or layout of components accommodated within the housing. This leads to a limited configuration of the housing.
Meanwhile, there is a demand to provide an airbag inflator adapted to control a timing of discharge of gas from the inflator depending upon various factors such as severity of the vehicle collision, position of the occupant, size of the occupant's body, and the like.